Industrial machines such as those used in construction and mining must often operate on uneven terrain. Not only must such machines be able to traverse, climb and descend steep slopes, but they must also be able to remain stationary on such terrain when appropriate. For example, according to one standard, the machine must be able to remain stationary on a predetermined grade while in second gear. For this reason, such machines are generally equipped with a parking brake that essentially locks the machine's wheels or other ground-engaging elements.
At the same time, for safety reasons, it is sometimes necessary for industrial machines to “drive through” the parking brake in first gear. In other words, when the parking brake is set and the machine is stationary, the operator should be able to force some movement of the machine in first gear, overriding the parking brake.
Thus, parking brakes for industrial machines need to be of sufficient holding power to serve their primary goal, i.e., that of holding the machine stationary, while not being so strong as to prevent the operator from moving the machine in first gear. As such, the maximum holding power of the parking brake is limited by the amount of propulsive torque available to drive through the parking brake in first gear.
An approach to this problem may be to weaken the parking brake until it has insufficient holding power to stop movement of the machine when in first gear under normal operation. However, in some circumstances, this will also yield a parking brake that is too weak to meet other holding power requirements. Similarly, providing a parking brake that is strong enough to meet other holding requirements, e.g., holding the machine stationary in second gear while on a predetermined grade, may yield a brake that cannot be overridden in first gear.
The present disclosure is directed to a system and method that mitigate certain of the noted deficiencies. However, it should be appreciated that the solution of any existing problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent expressly claimed. Additionally, this background section discusses observations made by the inventors; the inclusion of any observation in this section is not an indication that the observation represents known prior art.